Hydrophobic catalytic materials and method of forming the same

ABSTRACT

A catalytic composition and method of making the same in which a catalytic material has an average pore size distribution sufficiently large to substantially prevent capillary condensation.

FIELD OF THE INVENTION

[0001] The present invention is directed to a method of treatingpollutant-containing gases in which such gases are contacted with acatalyst composition containing at least one catalytic material whichhas an average pore size and surface area sufficient to prevent or atleast substantially reduce capillary condensation.

BACKGROUND OF THE INVENTION

[0002] The present invention is directed to a method of formingcatalytic materials in such a manner that the catalytic material doesnot substantially undergo capillary condensation. Accordingly, theadverse effect that water vapor has on catalytic activity of thecatalytic material is minimized.

[0003] Catalytic materials, especially for removing pollutants from apollutant-containing gas are generally comprised of metals as well asother constituents which actively induce a chemical reaction. Theeffectiveness of a catalytic material depends in part on theavailability of catalytically active sites. The more catalyticallyactive sites available from a given catalyst, the more efficiently thecatalytic material can promote the desired reaction.

[0004] Catalytic materials are used to induce the reaction of pollutantscontained within a pollutant-containing gas into harmless by-products.There are numerous pollutants which are found in the atmosphere and/orcontained within gas discharged from industrial facilities or automotivevehicles. Such pollutants include hydrocarbons, carbon monoxide, ozone,sulfur compounds and NO_(x) compounds.

[0005] If a potentially catalytically active site is blocked then itsavailability to catalyze the chemical reaction of a pollutant iseliminated or at least substantially reduced. Compounds which blockcatalytically active sites do so by binding to the catalytic material sothat at least a portion of the time the catalytically active site isunavailable for catalyzing a reaction. The stronger the bond between theblocking compound and the catalytically active site, the less efficientthe catalytic material is in inducing a chemical reaction to convertpollutants to harmless by-products.

[0006] It is well known that water molecules have an affinity forcatalytic materials, especially metals. Accordingly, water serves as ablocking compound which reversibly binds to catalytically active sites.The bond between water molecules and catalytically active sites istypically of moderate strength so that the water molecules spend only aportion of the time bound to the catalytically active site. When thewater molecule is so bound, the particular catalytically active site isincapable of inducing a chemical reaction to convert pollutants toharmless by-products.

[0007] Catalytic materials including those incorporating preciousmetals, base metals and the like are employed in catalytic compositionsfor the treatment of pollutant-containing gases such as exhaust gas fromautomotive vehicles. The exhaust gases typically contain moisture orwater vapor and the amount of water vapor will vary depending onclimatic conditions. As previously indicated, the presence of watermolecules can impede the effectiveness of a catalytic material becausewater acts as a blocking compound.

[0008] During normal operation of an automotive vehicle, the temperatureof the exhaust gas will be several hundred degrees. Under these hightemperature conditions, water molecules are energized due to the inputof thermal energy. Highly energized molecules tend to remain in motion.This high energy level limits the time the water molecules remain boundto catalytically active sites. Accordingly, the presence of water vaporunder high temperature operating conditions does not adversely affectthe efficiency of catalytic materials to the same extent as under lowertemperature operating conditions when water molecules are lessenergized. Under less energized conditions, water molecules tend to bindto catalytically active sites for a greater length of time than underhigh energy conditions (e.g. higher temperatures).

[0009] Catalytic materials are generally manufactured with a preferencefor high surface areas so as to enable a greater number of catalyticsites to catalyze the reaction of pollutants contained within apollutant-containing gas. High surface area catalytic materials can beproduced by employing a pore structure comprised of micropores having anaverage pore size as low as possible, typically less than 5 nanometers(nm). Smaller pores therefore, are characteristic of high surface areacatalytic materials.

[0010] It has been observed that catalytic materials having an averagepore size of less than about 5 nm, undesirably retain moistureespecially under high humidity and low temperature (i.e. low energy)conditions. When water vapor is in contact with such materials,molecules of water enter the relatively small pores and remain withinthe pores. This phenomenon is known as capillary condensation.

[0011] “Capillary condensation” as used herein means that watermolecules enter and remain within the micropore structure of thecatalytic material. Because the micropores have very small pore sizes(typically less than 5 nm), the water molecules become “stuck” in thepores and can be removed only with some difficulty. The retention ofwater molecules in micropores (capillary condensation) reduces theeffectiveness of catalytic materials because the water molecules blockthe catalytically active sites as previously described. In particular,the number of catalytically active sites available to catalyze thereaction of a pollutant is reduced and therefore the efficiency of thecatalytic material is impaired.

[0012] It would therefore be a significant advance in the art ofremoving pollutants from a pollutant-containing gas to provide catalyticmaterials in which capillary condensation is prevented or at leastsubstantially minimized. It would be another advance in the art toproduce catalytic materials which can be used in automotive vehicles toremove pollutants from a pollutant-containing gas under high humidityand/or low temperature operating conditions.

SUMMARY OF THE INVENTION

[0013] The present invention is generally directed to a method oftreating a pollutant-containing gas with a catalytic material in whichthe presence of water vapor, even under high relative humidityconditions and/or low temperature operating conditions, does notsubstantially adversely affect catalyst performance. Catalytic materialswhich can perform in this manner are also encompassed by the presentinvention.

[0014] In particular, the present invention is directed to a catalyticcomposition and method of treating a pollutant-containing gas comprisingcontacting the pollutant-containing gas with a catalyst compositioncontaining at least one catalytic material which has an average poresize of at least 5 nm and a surface area sufficiently large to enablethe catalytic material to react with the pollutant in thepollutant-containing gas. As a result capillary condensation is at leastsubstantially prevented whereby there is sufficient accessability of thecatalytically active sites to induce a reaction of the pollutant toproduce harmless by-products.

[0015] In a preferred form of the invention, there is provided a methodof treating a pollutant-containing gas even under high humidity and/orreduced temperature conditions in which the catalytic material has anaverage pore size of at least 10 nm. Catalytic materials employed in thepresent method are also the subject of the present invention.

[0016] The catalytic material, in addition to having an average poresize of at least 5 nm distribution as described above, also has arelatively large surface area, typically at least 100 m²/g. Preferably,the catalytic material has a relatively high total pore volume,typically at least 0.9 cm³/g.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The following drawings are illustrative of embodiments of theinvention and are not intended to limit the invention as encompassed bythe claims forming part of the application.

[0018]FIG. 1 is a graph showing the amount of water adsorbed by twocatalysts as a function of relative humidity;

[0019]FIG. 2 is a graph showing capillary condensation as a function ofaverage pore size for a given catalytic material; and

[0020]FIG. 3 is a graph showing the efficiency of ozone conversion as afunction of relative humidity.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The catalytic materials of the present invention have an averagepore size and a surface area sufficient to prevent or at leastsubstantially reduce capillary condensation. In a preferred form of theinvention, the total pore volume of the catalytic material is selectedto further minimize capillary condensation. As previously explained,capillary condensation occurs when water molecules enter micropores of acatalytic material and become retained therein because the small size ofthe pores makes it difficult for the water to be removed in the absenceof raising the energy level of the water molecules such as occurs atelevated temperatures (e.g. temperatures of at least about 100° C.). Asused herein the term “average pore size” shall mean the average porediameter of the pores of the catalytic material.

[0022] It has been observed that condensation of water occurs in thepores of catalytic materials having an average pore size of less than 5nm, especially at a relative humidity of at least about 50%. Therelative humidity is based on the partial pressure of the water in theair and the saturation vapor pressure at the catalyst operatingtemperature. The filing of pores with water molecules via capillarycondensation is governed by the formula${{{RT}\quad {\ln \left( \frac{P}{P} \right)}} = \frac{{- V}\quad \gamma \quad \cos \quad (\theta)}{D}},$

[0023] where R is the gas constant (8.31 Joules/mole/K), T is theoperating temperature of catalyst system, ln is the natural logarithm, Pis the partial pressure of water vapor, P₀ is the saturation vaporpressure of water at the operating temperature T, V is the molar volumeof water (18 cm³/mole), γ is the surface tension of water (72.6dynes/cm), θ is the contact angle and D is the capillary diameter (cm).The contact angle is the angle formed between the liquid surface and asolid surface. For hydrophilic surfaces, the contact angle is generallybetween about 0 and 90 degrees. For hydrophobic surfaces, the contactangle is generally between about 90 and 180 degrees. The contact anglefor metal oxide surfaces (e.g. alumina) is typically less than 90°.

[0024] Applicants have discovered that when a catalytic material isprovided with an average pore size of at least 5 nm and a surface areaof at least 100 m²/g capillary condensation is prevented or at leastsubstantially reduced.

[0025] Referring to FIG. 1 there is shown a graph depicting therelationship between water adsorption and relative humidity for twodifferent manganese oxide based catalytic materials. The first of thecatalytic materials is Carulite® 200 produced by Carus Chemicals, Inc.and the second is HSA (a high surface area) MnO₂ produced by Chemetals,Inc. As shown in FIG. 1, water adsorption for each of the catalyticmaterials is relatively low until the relative humidity reaches about50%. Water adsorption below a relative humidity of about 50% is dueprincipally to multi-layer adsorption. Multilayer adsorption is theformation of multiple thin layers of moisture which does notsubstantially prevent access of the pollutant-containing gas to thecatalytic material contained within the pores. At a, relative humidityof about 50%, the amount of water adsorbed increases significantly dueto capillary condensation.

[0026] In accordance with the present invention, the average pore sizeand the relative humidity of the atmosphere impact on whether or notcapillary condensation occurs.

[0027] As shown in FIG. 2 and in accordance with the present invention,as the average pore size increases, the relative humidity necessary toinduce capillary condensation significantly increases. Capillarycondensation is initiated at low pore sizes (an average pore size ofless than 5 nm) at low relative humidity conditions (i.e. ≦50%). Thusincreasing the average pore siZe to at least 5 nm prevents orsubstantially reduces capillary condensation to relative humidities ofup to about 50% when the catalytic material has a surface area of atleast 100 m²/g. Increasing the average pore size to a preferred range ofat least 10 nm and more preferably from about 15 to 50 nm substantiallyeliminates capillary condensation to relative humidities up to about75%.

[0028] The effect of relative humidity on the ability of a catalyst toconvert ozone to harmless byproducts is shown in FIG. 3. These resultswere obtained by passing 1.53 L/min of air containing 5 ppm of ozonethrough 50 mg of high surface area α-MnO₂ at 25-27° C. As shown in FIG.3, about 65-68% conversion of ozone was achieved at a relative humidityof from about 50 to 60%. However, as the relative humidity increased,especially above 60% (e.g. 90%) there was a noticeable decline in theozone conversion rate to 19%. The significant decline in conversion rateis due at least in large part to the presence of water in vicinity ofthe catalytically active sites due to capillary condensation.

[0029] The catalytic materials which can be employed in the presentinvention can vary widely but generally include platinum group metals,base metals, alkaline earth metals, rare earth metals and transitionmetals.

[0030] The platinum group metals include platinum, palladium, iridium,and rhodium. The base metals include manganese, copper, nickel, cobalt,silver and gold. The alkaline earth metals include beryllium, magnesium,calcium, strontium, barium, and radium. The rare earth metals includecesium, praseodymium, neodymium, promethium, samarium, europium,gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium,and lutetium. Early transition metals include scandium, yttrium,lanthanum, tympanum, zirconium, and hafnium.

[0031] Examples of such catalytic materials are disclosed in U.S. Pat.No. 5,139,992, U.S. Pat. No. 5,128,306, U.S. Pat. No. 5,057,483, U.S.Pat. No. 5,024,981, U.S. Pat. No. 5,254,519, and U.S. Pat. No.5,212,142, each of which is incorporated herein by reference.

[0032] The most preferred catalytic materials for use in the presentinvention are those which contain manganese and particularly those whichcontain manganese dioxide as explained in detail hereinafter. Suchcatalytic materials are especially suitable for treating ozone.

[0033] Ozone treating catalyst compositions comprise manganese compoundsincluding manganese dioxide, non stoichiometric manganese dioxide (e.g.,XMnO_((1.5-2.0))), and/or XMn₂O₃ wherein X is a metal ion, preferably analkali metal or alkaline earth metal (e.g. sodium, potassium andbarium). Variable amounts of water (H₂O, OH⁻) can be incorporated in thestructure as well. Preferred manganese dioxides, which are nominallyreferred to as MnO₂ have a chemical formula wherein the molar ratio ofmanganese to oxide is about from 1.5 to 2.0. Up to 100 percent by weightof manganese dioxide MnO₂ can be used in catalyst compositions to treatozone. Alternative compositions which are available comprise manganesedioxide and compounds such as copper oxide alone or copper oxide andalumina. In accordance with the present invention, the most dramaticimprovement in catalytic efficiency with higher pore size distributionis seen with catalyst containing manganese dioxide alone.

[0034] Useful and preferred manganese dioxides are alpha-manganesedioxides nominally having a molar ratio of manganese to oxygen of from 1to 2. Useful alpha manganese dioxides are disclosed in U.S. Pat. No.5,340,562 to O'Young, et al.; also in O'Young, Hydrothermal Synthesis ofManganese Oxides with Tunnel Structures presented at the Symposium onAdvances in Zeolites and Pillared Clay Structures presented before theDivision of Petroleum Chemistry, Inc. American Chemical Society New YorkCity Meeting, Aug. 25-30, 1991 beginning at page 342; and in McKenzie,the Synthesis of Birnessite, Cryptomelane, and Some Other Oxides andHydroxides of Manganese, Mineralogical Magazine, December 1971, Vol. 38,pp. 493-502. For the purposes of the present invention, the preferredalpha-manganese dioxide is selected from hollandite (BaMn₈O₁₆.xH₂O),cryptomelane (KMn₈O₁₆.xH₂O), manjiroite (NaMn₈O₁₆.xH₂O) or coronadite(PbMn₈O₁₆.xH₂O).

[0035] The manganese dioxides useful in the present invention preferablyhave a surface area as high as possible while maintaining a pore sizedistribution of at least 10 nm. A preferred surface area is at least 100m²/g.

[0036] The composition preferably comprises a binder as of the typedescribed below with preferred binders being polymeric binders. Thecomposition can further comprise precious metal components with preciousmetal components being the oxides of precious metal, including theoxides of platinum group metals and oxides of palladium or platinum alsoreferred to as palladium black or platinum black. The amount ofpalladium or platinum black can range from 0 to 25%, with useful amountsbeing in ranges of from about 1 to 25 and 5 to 15% by weight based onthe weight of the manganese component and the precious metal component.

[0037] It has been found that the use of compositions comprising thecryptomelane form of alpha manganese oxide, which also contain apolymeric binder can result in greater than 50%, preferably greater than60% and typically from 75-85% conversion of ozone in a concentrationrange of up to 400 parts per billion (ppb).

[0038] The preferred cryptomelane manganese dioxide has a crystallitesize ranging from 2 to 10 nm and preferably less than 5 nm. It can becalcined at a temperature range of from 250° C. to 550° C. andpreferably below 500° C. and greater than 300° C. for at least 1.5 hoursand preferably at least 2 hours up to about 6 hours.

[0039] The preferred cryptomelane can be made in accordance with methodsdescribed and incorporated into U.S. patent application Ser. No.08/589,182 filed Jan. 19, 1996 (Attorney Docket No. 3777C), incorporatedherein by reference. The cryptomelane can be made by reacting amanganese salt including salts selected from the group consisting MnCl₂,Mn(NO₃)₂, MnSO₄ and Mn (CH₃COO)₂ with a permanganate compound.Cryptomelane is made using potassium permanganate; hollandite is madeusing barium permanganate; coronadite is made using lead permanganate;and manjiroite is made using sodium permanganate. It is recognized thatthe alpha-manganese dioxide useful in the present invention can containone or more of hollandite, cryptomelane, manjiroite or coronaditecompounds. Even when making cryptomelane minor amounts of other metalions such as sodium may be present. Useful methods to form thealpha-manganese dioxide are described in the above references which areincorporated herein by reference.

[0040] The preferred alpha-manganese dioxide for use in accordance withthe present invention is cryptomelane. The preferred cryptomelane is“clean” or substantially free of inorganic anions, particularly on thesurface. Such anions could include chlorides, sulfates and nitrateswhich are introduced during the method to form cryptomelane. Analternate method to make the clean cryptomelane is to react a manganesecarboxylate, preferably manganese acetate, with potassium permanganate.

[0041] It is believed that the carboxylates are burned off during thecalcination process. However, inorganic anions remain on the surfaceeven during calcination. The inorganic anions such as sulfates can bewashed away with the aqueous solution or a slightly acidic aqueoussolution. Preferably the alpha manganese dioxide is a “clean” alphamanganese dioxide. The cryptomelane can be washed at from about 60° C.to 100° C. for about-one-half hour to remove a significant amount ofsulfate anions. The nitrate anions may be removed in a similar manner.The “clean” alpha manganese dioxide is characterized as having anIR-spectrum as disclosed in U.S. patent application Ser. No. 08/589,182filed Jan. 19, 1996.

[0042] A preferred method of making cryptomelane useful in the presentinvention comprises mixing an aqueous acidic manganese salt solutionwith a potassium permanganate solution. The acidic manganese saltsolution preferably has a pH of from 0.5 to 3.0 and can be made acidicusing any common acid, preferably acetic acid at a concentration of from0.5 to 5.0 normal and more preferably from 1.0 to 2.0 normal. Themixture forms a slurry which is stirred at a temperature range of from50° C. to 110° C. The slurry is filtered and the filtrate is dried at atemperature range of from 75° C. to 200° C. The resulting cryptomelanecrystals have a surface area of typically in the range of at least 100m²/g.

[0043] Catalytic materials with an average pore size of at least 5 nm inaccordance with the present invention can be made, for example, by heattreating the material after crystallization. The post-crystallizationmaterial can be heated to temperatures sufficient to increase theaverage pore size to at least 5 nm. In most cases, thepost-crystallization heat-treating temperature is in the range of fromabout 300 to 500° C.

[0044] Other useful compositions comprise manganese dioxide andoptionally copper oxide and alumina and at least one precious metalcomponent such as a platinum group metal supported on the manganesedioxide and where present copper oxide and alumina. Useful compositionscontain up to 100, from 40 to 80 and preferably 50 to 70 weight percentmanganese dioxide 10 to 60 and typically 30 to 50 percent copper oxide.Useful compositions include hopcalite (supplied by, for example, MineSafety Applications, Inc.) which is about 60 percent manganese dioxideand about 40 percent copper oxide; and Carulite® 200 (sold by CarusChemical Co.) which is reported to have 60 to 75 weight percentmanganese dioxide, 11 to 14 percent copper oxide and 15 to 16 percentaluminum oxide. The surface area of Carulite® 200 is reported to beabout 180 m²/g. Calcining at 450° C. reduces the surface area of theCarulite® by about fifty percent (50%) without significantly affectingactivity. It is preferred to calcine manganese compounds at from 300° C.to 500° C. and more preferably 350° C. to 450° C. Calcining at 550° C.causes a great loss of surface area and ozone treatment activity.Calcining the Carulite® after ball milling with acetic acid and coatingon a substrate can improve adhesion of the coating to a substrate.

[0045] Other compositions to treat ozone can comprise a manganesedioxide component and precious metal components such as platinum groupmetal components. While both components are catalytically active, themanganese dioxide can also support the precious metal component. Theplatinum group metal component preferably is a palladium and/or platinumcomponent. The amount of platinum group metal compound preferably rangesfrom about 0.1 to about 10 weight percent (based on the weight of theplatinum group metal) of the composition. Preferably, where platinum ispresent it is present in amounts of from 0.1 to 5 weight percent, withuseful and preferred amounts on pollutant treating catalyst volume,based on the volume of the supporting article, ranging from about 0.5 toabout 70 g/ft³. The amount of the palladium component preferably rangesfrom about 2 to about 10 weight percent of the composition, with usefuland preferred amounts on pollutant treating catalyst volume ranging fromabout 10 to about 250 g/ft³.

[0046] Various useful and preferred pollutant treating catalystcompositions, especially those containing a catalytically activecomponent such as a precious metal catalytic component, can comprise asuitable support material such as a refractory oxide support. Thepreferred refractory oxide can be selected from the group consisting ofsilica, alumina, titania, ceria, zirconia and chromia, and mixturesthereof. More preferably, the support is at least one activated, highsurface area compound selected from the group consisting of alumina,silica, titania, silica-alumina, silica-zirconia, alumina silicates,alumina zirconia, alumina-chromia and alumina-ceria. The refractoryoxide can be in suitable form including bulk particulate form typicallyhaving particle sizes ranging from about 0.1 to about 100 and preferably1 to 10 μm or in sol form also having a particle size ranging from about1 to about 50 and preferably about 1 to about 10 nm. A preferred titaniasol support comprises titania having a particle size ranging from about1 to about 10, and typically from about 2 to 5 nm.

[0047] Also useful as a preferred support is a coprecipitate of amanganese oxide and zirconia. This composition can be made as recited inU.S. Pat. No. 5,283,041, incorporated herein by reference. Thecoprecipitated support material preferably comprises in a ratio based onthe weight of manganese and zirconium metals from about 5:95 to 95:5;preferably from about 10:90 to 75:25; more preferably from about 10:90to 50:50; and most preferably from about 15:85 to 50:50. A useful andpreferred embodiment comprises a Mn:Zr weight ratio of about 20:80. U.S.Pat. No. 5,283,041 describes a preferred method to make a coprecipitateof a manganese oxide component -and a zirconia component. A zirconiaoxide and manganese oxide material may be prepared by mixing aqueoussolutions of suitable zirconium oxide precursors such as zirconiumoxynitrate, zirconium acetate, zirconium oxychloride, or zirconiumoxysulfate and a suitable manganese oxide precursor such as manganesenitrate, manganese acetate, manganese dichloride or manganese dibromide,adding a sufficient amount of a base such as ammonium hydroxide toobtain a pH of from about 8 to 9, filtering the resulting precipitate,washing with water, and drying at a temperature of from about 450° C. to500° C.

[0048] A useful support for a catalyst to treat ozone is selected from arefractory oxide support, preferably alumina and silica-alumina with amore preferred support being a silica-alumina support comprising fromabout 1% to 10% by weight of silica and from about 90% to 99% by weightof alumina.

[0049] The average pore size of the catalytic material including thepreferred materials described above is at least 5 nm, preferably atleast 10 nm, more preferably from about 15 to 50 nm. At this averagepore size, any water molecules which enter the pores are readilydisengaged from catalytic sites without the imposition of excessiveenergy such as thermal energy. Accordingly, the method of the presentinvention is particularly suited to the catalytic conversion of apollutant-containing gas (e.g. exhaust gas) at reduced operatingtemperatures. The method of the present invention is particularly suitedto the efficient and effective conversion of pollutants to harmlessby-products when an engine of an automotive vehicle is under startupconditions (i.e. generally less than 45° C.). The catalytic materials ofthe present invention are particularly suited for the conversion ofcarbon monoxide and ozone.

EXAMPLE 1

[0050] 61 grams of a powdered catalytic material containingnoncrystalline KMn₈O₆ prepared by methods described in “MicrostructuralStudy of Hollandite-type Mn0₂ Nano-fibers” M. Benaissa et al. App.Physics Letters, Vol. 70, No. 16, pp.2120-2122 (1997) and “NickelHydroxide and other Nanophase Cathode Materials For RechargeableBatteries” D. E. Reisner et al. J. Power Sources Vol. 65, No. 1-2, pp.231-233 (1997) was treated in the following manner. The material iscomprised of primary crystallites having a fibrous shape with aspectratios of about 10:1 (i.e. 10-100 nm wide×100-1,000 nm long). Thefibrous crystallites form loosely compacted subspherical agglomeratesresembling nests up to about 10 μm across. The bulk of density of thematerial is about 0.3 to 0.6 g/cm³. The powder was pressed, granulatedand sized so that the resulting material had an average pore size of32.2 nm, a pore volume (the total volume divided by the average poresize) of 0.98 cm³/g and a surface area of 122 m²/g. Equal volumes (0.13cm³) of the powder were loaded into glass tubes and secured into a bedwith glass wool. The samples were run on a temperature and humiditycontrolled flow reactor equipped with an ozone generator and UV ozoneanalyzer.

[0051] A gas containing 5 ppm of ozone in air was passed through thesample bed at a space velocity of 150,000 hr⁻¹ at 45° C. with a dewpoint of 17° C. for 2 hours. The instantaneous conversion of ozone tooxygen at the end of two hours is shown in Table 1. TABLE 1 SURFACE POREAVG. PORE OZONE AREA^(a), VOLUME^(b), DIAMETER CONVERSION m²/g cm³/g nm% SAMPLE MASS EXAMPLE 1 122 0.98 32.2 99  61 mg COMPARATIVE 44 0.21 18.699  91 mg EXAMPLE 1 COMPARATIVE 84 0.20 9.4 72 135 mg EXAMPLE 2 (1.3 hr)

[0052] As shown in Table 1, the % conversion of ozone for Example 1 was99%. This example employed an average pore diameter and surface areawhich minimized capillary condensation. The % conversion was achievedwith a low mass of catalytic material.

COMPARATIVE EXAMPLE 1

[0053] 91 grams of a starting material containing activated MnO₂obtained from Johnson Matthey Alfa Aesar (Technical Grade Stock No.14340) was comprised of nearly equant or subspherical crystallites withdiameters of from about 50 to 100 nm. The crystallites form denseaggregates and agglomerates up to about 20 μm across. The bulk densityof this material is from about 1.1 to 1.3 g/m². The final catalyticmaterial was obtained by heating the starting material to 450° C. for 2hours to obtain an average pore size distribution of 18.6 nm.

[0054] As shown in Table 1 the % conversion of ozone initiated by thecatalytic material was 99%. However, a larger mass of catalytic materialwas needed to achieve high conversion rates due to the relatively smallsurface area (44 m²/g) and pore volume (0.21 cm³/g) as compared to thecatalytic material of Example 1.

COMPARATIVE EXAMPLE 2

[0055] The same catalytic material employed in Comparative Example 2 wasused except that the step of heating to 450° C. was omitted. Theresulting material was comprised of nearly equant or subsphericalcrystallites on the order of about 5 to 25 nm across that formsubspherical aggregates and agglomerates up to 20 μm across, with anaverage pore size distribution of 9.4 nm. The bulk density of thematerial is between 0.9 and 1.1 g/cm³.

[0056] The catalytic material was treated in the same manner as inExample 1 and Comparative Example 2 except that the reaction wasterminated after 1.3 hours because the conversion rates were decreasing.The results of this comparative example showing the effectiveness ofconverting ozone to oxygen is shown in Table 1. The conversion rate forthis comparative Example was only 72% despite using more than twice theamount of the catalytic material.

[0057] As shown in Table 1, the highest conversion rate with the lowestmass of material is achieved when the catalytic material (Example 1) hasan average pore size equal to or exceeding about 5.0 nm, a pore volumeequal to or exceeding about 0.9 cm³/g and a surface area equal to orexceeding 100 m²/g.

[0058] As further shown in Table 1, the comparative examples showedsignificantly lower conversion rates for even greater masses ofmaterial.

What is claimed is:
 1. A catalytic composition for catalyzing a reactionof a pollutant-containing gas comprising at least one catalytic materialhaving an average pore size of at least 5 nm and a surface areasufficiently large to enable the catalytic material to react with thepollutant in said pollutant-containing gas.
 2. The catalytic material ofclaim 1 wherein the one catalytic material has an average pore size isat least 10 nm.
 3. The catalytic material of claim 2 wherein the averagepore size is from about 15 to 50 nm.
 4. The catalytic material of claim1 wherein the catalytic material includes manganese oxide.
 5. Thecatalytic material of claim 1 wherein the catalytic material issubstantially manganese oxide.
 6. The catalytic material of claim 5wherein the catalytic material includes XMn₈O₁₆ wherein X is a metalion.
 7. The catalytic material of claim 6 wherein X is selected from thegroup consisting of alkali metals and alkaline earth metals.
 8. Thecatalytic material of claim 6 wherein X is potassium.
 9. The catalyticmaterial of claim 1 wherein the surface area is at least 100 m²/g. 10.The catalytic material of claim 1 having a pore volume of at least 0.9cm³/g.
 11. The catalytic material of claim 1 having a pore volume of atleast 0.9 cm³/g and a surface area of at least 100 m²/g.
 12. A method oftreating a pollutant-containing gas comprising contacting thepollutant-containing gas with at least one catalytic material capable ofreacting with a pollutant in said gas, said catalytic material having anaverage pore size distribution sufficiently large to substantiallyprevent capillary condensation.
 13. The method of claim 12 wherein thecatalytic material has an average pore size distribution of at least 10nm.
 14. The method of claim 13 wherein the average pore sizedistribution is from about 15 to 50 nm.
 15. The method of claim 12wherein the catalytic material includes a manganese oxide.
 16. Themethod of claim 15 wherein the catalytic material is substantiallymanganese oxide.
 17. The method of claim 15 wherein the catalyticmaterial includes XMn₈O₁₆ wherein X is selected from the groupconsisting of alkali metals and alkaline earth metals.
 18. The method ofclaim 17 wherein X is potassium.
 19. The method of claim 12 wherein thecatalytic material has a surface area of at least 100 m²/g.
 20. Themethod of claim 12 wherein the catalytic material has a pore volume ofat least 0.9 cm³/g.
 21. The method of claim 13 wherein the catalyticmaterial has a pore volume of at least 0.9 cm³/g and a surface area ofat least 100 m²/g.
 22. A method of treating a pollutant-containing gascomprising contacting the pollutant-containing gas with the catalyticcomposition of claim
 1. 23. A method of treating a pollutant-containinggas comprising contacting the pollutant-containing gas with thecatalytic composition of claim
 2. 24. A method of treating apollutant-containing gas comprising contacting the pollutant-containinggas with the catalytic composition of claim
 3. 25. A method of treatinga pollutant-containing gas comprising contacting thepollutant-containing gas with the catalytic composition of claim
 9. 26.A method of treating a pollutant-containing gas comprising contactingthe pollutant-containing gas with the catalytic composition of claim 10.27. A method of treating a pollutant-containing gas comprisingcontacting the pollutant-containing gas with the catalytic compositionof claim 11.